Chat app with ionic and java server side (RESTful or Socket communication) ? need your explanation

i’m going to develop real time chat app with (private and group chat just with text , setting profile , message history , ) ionic 1 and angular 1 so i have java backend server,
so how can this chat app communicate with java server to send and receive msg …?.
in my opinion Client side application will communicate with server-side through REST calls !
or there is another way like socket or else ?
plz Help me with some explanation

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